Plastic circuit breakers are electrical appliances for the overload and short-circuit maintenance of low-voltage three-phase four-wire 220/380V circuits. Its interruption can generally be lower than the all-purpose circuit breaker, suitable as a low-voltage circuit and motor two, three, four maintenance devices; In addition, due to its small number of pairs of auxiliary contacts, it is not suitable for active operation to maintain electrical equipment, or a one-time remote cut off circuit. Electrical appliances maintained by low-voltage circuit breakers are not suitable for more than 4 levels from the main circuit breaker to the end. Otherwise selectivity would be lost. The current level of the additional current In is usually not regulated, and the additional current Inm each frame has a certain step of the circuit breaker additional current In to match it. The following, DZ20Y type Inm = 100A for example, In for 16A, 20A, 32A, 40A, 50A, 63A, 80A, 100A these 8 stages, but need to know Inm.

How to choose a low voltage measurement second or third level circuit breaker, also need to pay attention to the following aspects.

Short-circuit current Id of this distribution system; Distribution lines or motors should be able to operate overload

frequent starting and reverse connection braking of high-powered heavy-load motors.

There are many factors that are not conducive to safe and reliable operation, such as the operating ambient temperature of the circuit breaker.

Usually, after judging the additional current Inm of the circuit breaker casing, In is suitable for selecting a grade larger than the calculated current of the line, and it is also necessary to consider the time/current characteristics and selectivity of the overcurrent maintenance striker of the additional current In of the upper and lower level circuit breakers. Plastic case low-voltage circuit breaker selection should be calibrated for the following functional indicators.

1. Additional voltage: AC240V, AC400V, AC415V, AC500V, AC690V, DC250V.

2.Plastic case additional current Inm :Each brand series additional current level is different, need to browse the specific selection brand (such as Shanghai Taisi Electric) material after selection.

3.Additional current of circuit breaker In : The additional current level of each brand series is different, and should be selected according to the depicted load current of the distribution line or motor power and the skill data of the selected product.

4. Additional operating breaking talent Ics : In general, the higher the level of circuit breaker products the greater the breaking talent, you need to choose according to the level of power supply load and the type of building and financial burden, breaking talent is high quality products.

5. Additional limit breaking talent Icu:Icu is equal to 0.5-1 times of Ics. This means that it is no longer reapplied after being split by the limit value.

6. Additional short-time withstand current ICW:The overload current withstood at 1s, which does not affect the continuous use of the circuit breaker.

7. Number of poles: the number of poles varies from one series of products to another, generally 2-4 poles.

8. Overcurrent maintenance decoupling time/current characteristic curve: each series characteristic curve is different, which is an important parameter for people to selective consideration of the main points of the upper and lower level circuit breaker measures. The time of decoupling is inversely proportional to the multiple of additional current overload measures, and requires careful reading of the materials required to select product skills before making a judgement.

9 . Machine life number: the machine life number varies from series to series and is directly proportional to the level of quality of the circuit breaker, with a normal number of operations of 3000-25000.

10. Electrical life number: The electrical life number of each series of products is different, inversely proportional to the additional capacity of the moulded case circuit breaker and directly proportional to the quality level of the circuit breaker, with a normal number of operations of 1000-5000 times.

11. Case type circuit breaker device mode: circuit breaker is generally straightening fixed device.

12. Shell volume scale) The volume scale of each series varies greatly, and the product sample materials of each series need to be examined. The number of auxiliary contacts of the circuit breaker should be checked to meet the needs of the distribution system.